No, You can't have traps for both the tub and the shower on the same trap arm and vent.

You could use a double fixture fitting and have two trap arms,
For more room, put the fixture fitting at a 45 angle and use a s45 on the bottom and a s45 on the top to bring it back to verical.

Or you could use a wye on the lway back to the wall and come up with two santees, one for the shower and one for the tub.

If only you could drop below the ceiling and replace the 90 el with a santee fitting and come up sooner for the shower and tub fittings.

On the previous drawing you you had, when venting with a wye, you just need to roll it a bit when pulling off the vent. The idea is to have the lower part of the 2" vent higher than the flow line of the pipe it's venting.

yes it is, and I know, this in fact is what is raining on this whole bathroom parade.

thats one of the reasons this is such a difficult layout. I wish some one would have told the original "plumbers" that chopping up trusses is not a good idea. I have had to patch them (which is not ideal) in 2 places where the "plumber" cut a 4" (or really a group of 3 2") holes in them. Luckily its a double truss and one of them is only cut in one place on the top plate which is fixable. I would replace them totally but cant because I don't have access to both of them. Depending on what it looks like once I get the other part of the floor up I might be able to replace one of them, at any rate I am adding another regardless.